1. Field of the Invention
The invention relates to a device for arresting/de-arresting a telescopically extensible section of a telescopic jib (i.e., boom) and a method for arresting/de-arresting these sections.
2. Description of Related Art
It is known to pin the individual sections of a telescopic jib. Pinning serves to relieve the load on a telescoping system once a section of the telescopic jib has been telescoped to a working position. For this pinning, individual pinning points must be provided.
Pinning points, however, are complicated to design, and are only provided in a limited number (e.g., two pinning points being placed for each extendable jib section) so that each telescopically extensible section has an equally limited number of working positions. It is only in these working positions that it is possible to make full use of the telescopic jib, (i.e., loading the telescopic jib to maximum permissible capacity). Between these two pinning points the individual sections cannot be pinned, and can only handle minor forces. As a result, only low loads may be lifted by the telescopic jib when a section is in an intermediate position. In addition, suitable length/position sensing instruments are required to bring the section to be pinned precisely into the position for pinning.
One such pinning system for a telescopic jib is described in European Patent 0 661 234 A1.